But candy isn't terribly nourishing in the long haul, and "Easy Virtue" has more on its addled mind than treats. Lurking beneath all the flounciness and fripperies is an attack on the British landed gentry. The chief battle of wills here is between Larita, who comes from humble Detroit stock, and Mrs. Whittaker, whose spine seems made not of steel but of plutonium. She's so formidable, and so disapproving of Larita as her new daughter-in-law, that the environs seem to ice up whenever she's around.

Most of those environs consist of the Whittakers' vast country estate, which also houses John's two simpering, resentful spinster sisters (Kimberley Nixon and Katherine Parkinson). Between the ogre-ish mother and sisters and that gloomily imposing estate, "Easy Virtue" has the trappings of a fairy tale, with Larita as a kind of flapper Red Riding Hood. But Mr. Whittaker is no big bad wolf. As Firth plays him, he's the only family member, and that includes John, who truly understands Larita. Still a bit shellshocked from his service in World War I, he carries a world weariness that is easily the most authentic emotion in a movie that otherwise overdoses on artificiality.

Biel, for example, is required to take her character through a full emotional arc from giddy to sorrowful, but she doesn't have the chops for it. Surprisingly, she's better at playing the serious stuff. It doesn't help that the director, Stephan Elliott, has saddled her with an unbecoming peroxide coif, though her outfits are museum quality.

Biel also can't quite manage the brittle witticisms she is often required to dispense (some of which aren't so witty anyway – Elliott and his co-screenwriter Sheridan Jobbins, often try, and fail, to out-Coward Noel Coward). This deficiency is particularly glaring in her matchups with Scott Thomas, who is a master of enunciated hauteur. It's interesting to compare her performance here with the one she gave last year as the ex-con in "I Loved You For So Long" – one is ice, the other was all banked fires.

The filmmakers work in contemporary songs redone in 1920s jazz renditions, but this ploy only serves to reinforce the film's faintly mildewed quality. Its high spirits are, for the most part, forced. One sequence in particular, about a squashed house pet, is dragged on for so long that the ASPCA should protest. (Don't worry, no real animals were harmed, though the actors don't get off scot-free.)

In this day and age, is it still possible – or even advisable – to make one of these upper-crust extravaganzas? The recent "Brideshead Revisited," with a towering performance by Emma Thompson, would seem to answer in the affirmative. Like that film, "Easy Virtue" has aspirations to be much more than a comedy. It wants to flay, if only with a penknife, the entire British class system. But in order to do that, you first need a credential in short supply here: a sense of class. Grade: C+ (Rated PG-13 for sexual content, brief partial nudity, and smoking throughout.)